Embodiments of the inventive concepts relate to memory devices, and more particularly, to memory devices configured to prevent read failure.
Semiconductor memory devices may be generally classified as volatile memory devices or nonvolatile memory devices. Read and write speeds of the volatile memory devices may be fast, but data stored therein may disappear when a power supply is interrupted. In contrast, the nonvolatile memory devices may retain data stored therein even though external the power supply is interrupted. Therefore, the nonvolatile memory devices may be used to store information to be retained regardless of whether power is supplied.
Demand for nonvolatile semiconductor memory devices capable of implementing high integration and large capacity is increasing. An example of nonvolatile semiconductor memory devices is flash memory used in portable electronic devices. However, some nonvolatile elements may be randomly accessible and may have improved performance. For example, ferroelectric RAM (FRAM) devices may use ferroelectric capacitors, magnetic RAM (MRAM) devices may use tunneling magneto-resistive (TMR) layers, phase change RAM (PRAM) devices may use chalcogenide alloys, resistive RAM (RRAM) devices may use variable resistance layers as a data storage medium, etc.
The above-described nonvolatile memories, in particular the MRAM, may include a reference cell for determining data stored in memory cells, in addition to a memory cell in which data is stored. However, a voltage (or resistance) distribution of memory cells in which data is stored may vary due to various causes, such as the number of unselected memory cells and a peripheral temperature. If a level of a reference voltage used to perform a read operation is not corrected even though the voltage distribution of memory cells varies due to the causes, serious read failure may be caused. Therefore, it may be important to prevent the read failure through correction of the reference voltage.